Various methods have been known for manufacturing carbon nanotubes, such as arc dischrge methods, laser ablation methods, thermal CVD methods, plasma CVD methods, and the like. Carbon nanotubes produced by arc discharge methods or laser ablation methods include both single wall carbon nanotube (SWNT: Single Wall Nanotube), which consists of a single graphene sheet, and multiple-wall carbon nanotube (MWNT: Multi-Wall Nanotube), which consists of a plurality of graphene sheets. In general, MWNTs are produced by thermal CVD methods and plasma CVD methods. In a SWNT, a graphene sheet, in which carbon atoms are bound to each other via a strong bond called an sp2 bond so as to form six-membered rings, is rolled into a tube with the end of the tube being closed by several six-membered rings together with five-membered rings.
A method for synthesizing carbon nanotubes in large amounts was proposed in Nature 358, 220 (1992). The product obtained by the method described in this literature contains, in addition to carbon nanotubes, a large amount of residual carbon impurities such as graphite-like material and amorphous carbon and, therefore, the carbon nanotubes have to be separated and purified. However, as carbon impurities have strong tendency to coagulate, it has been very difficult to isolate them completely.
Methods of purifying carbon nanotubes are disclosed in JP 8-231210 A, JP 2000-290008 A, JP 2002-515847, etc. All of these methods are post-processing methods to be performed after carbon nanotubes have been manufactured, and are not applicable to carbon nanotubes manufactured directly on a substrate.
Use of an alcohol such as ethanol or methanol as the carbon source for growing carbon nanotubes is described in S. Maruyama et al., Low-Temperature synthesis of high-purity single-walled carbon nanotubes from alcohol, Chem. Physics Letters 360 (2002), 229-234. It is stated that OH radicals produced upon decomposition of alcohol serve to effectively remove amorphous carbon, and thereby makes it possible to grow carbon nanotubes of high purity.
JP 2000-86218 A discloses a method of manufacturing carbon nanoubes by thermal cracking of aromatic hydrocarbons such as benzene or toluene, or aliphatic hydrocarbons such as naphtha or gas oil in the presence of a thermal cracking accelerator such as cyanuric acid.
Patent Document 1
JP 8-231210 A
Patent Document 2
JP 2000-290008 A
Patent Document 3
JP 2002-515847
Patent Document 4
JP 2000-86218 A
Non-Patent Document 1
Nature 358, 220 (1992)
Non-Patent Document 2
S. Maruyama et al., Low-Temperature synthesis of high-purity single-walled carbon nanotubes from alcohol, Chemical Physics Letters 360 (2002) 229-234